CORE B ABSTRACT The broad objective of the Nonhuman Primate (NHP) Core is to support the development of optimized formulation(s) for microbicide/biomedical prevention (MBP) delivery that result in reliable administration and sustained drug presence at specified target sites. Innovative approaches have been created to develop NHP models that more fully represent human use of any HIV prevention modality. Worldwide, HIV transmission is through sexual encounters and use of any topical product will need to be assessed in conjunction with sex. However, few laboratories have addressed this issue. To fill this critical gap, we have developed an NHP coital model and have already assessed product pharmacokinetics before and after coitus. Despite high seminal viral load associated with HIV transmission, not every sexual encounter results in infection. The repeat, low-dose (RLD) challenge NHP model more accurately recapitulates the human transmission kinetics. Moreover, use of the RLD model will allow for multiple viral exposures following a single dose of MK-2048 film providing a robust evaluation of efficacy. These NHP models, which more accurately portray the real world, will be utilized to determine the pharmacokinetics of MK-2048 when delivered in an extended release vaginal film, to establish the safety profile for film use in the presence and absence of coitus, and to assess the developed product?s potential efficacy in preventing HIV infection.